This application claims the priority of German application 197 49 296.7, filed Nov. 7, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for determining an initiation threshold value for an automatic braking process.
In an automatic braking process, a brake pressure is produced which is greater than the brake pressure which corresponds to the operation of the brake pedal by the driver.
DE 40 28 290 C1 discloses an automatic braking process of this type. DE 44 13 172 C1 discloses an example of the adaptation of the initiation threshold value as a function of the driving situation disclosed in DE 40 28 290 C1.
Furthermore, it is known to use sensors in order to detect the distance between the vehicle and a preceding vehicle and, if this distance is less than a certain limit, to implement a braking process which ensures that a safe distance is maintained between the vehicle and the preceding vehicle. Such a braking process is performed by using minor decelerations (i.e., with low brake pressures). This is performed, on the one hand, for reasons of convenience to prevent undesirable severe jerking of the vehicle. On the other hand, the braking process is implemented for reasons of traffic safety, i.e., to prevent drivers who are following too closely from being surprised by a brief, abrupt deceleration of the preceding vehicle which could lead to rear-impact accidents.
Nevertheless, short distances between vehicles present a risk of major accidents. In short, if a driver operates his brakes when there is a short distance between this vehicle and the preceding vehicle, in the vast majority of cases, the driver of the vehicle is often required to perform an emergency braking procedure due to the short distance between the vehicles.
It is therefore an object of the invention to improve the safety of vehicles by implementing an emergency braking procedure, as quickly as possible, when the distances between vehicles are short. This emergency braking process, within what is physically possible, ensures a rapid deceleration of the rear vehicle and thus helps to avoid rear-impact collision accidents.
This and other objects and advantages are achieved by the method according to the invention, in which during the automatic braking process, a brake pressure is produced which is greater than the brake pressure that corresponds to the actual position of the brake pedal. In essence, the automatic braking process is initiated whenever the rate of operation of the brake pedal exceeds an initiation threshold value. If the distance to the preceding vehicle is less than a predetermined limit, the distance to the preceding vehicle is detected and the initiation threshold value of the automatic braking process is reduced.
In an advantageous manner, this ensures that a safe and quick change of the initiation threshold value of the automatic braking process occurs if the driver operates the brake pedal during an emergency. As a further consequence, a brake pressure is produced which is greater than the brake pressure that corresponds to the actual position of the brake pedal.
In accordance with another objective of the invention, if the distance to the preceding vehicle is less than another predetermined limit value, an automatic braking process is performed, which is independent of the operation of the brake pedal by the driver. Here, the braking process is performed in an advantageous manner such that at least one wheel of the vehicle reaches the locking limit. In this case, the automatic braking process is advantageously terminated if either the distance to the preceding vehicle exceeds a predetermined value (due, for example, to the vehicle becoming stationary), or it is determined that the driver has released the brakes.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.